1. Technical Field
The present invention relates to an air throttle system for controlling not only the load output, but also the charge air motion and burn rate of a reciprocating internal combustion engine.
2. Description of Prior Art
In the interest of improving engine performance at high engine speeds, designers often increase, or at least desire to increase, the overlap between intake and exhaust valve events. Unfortunately, this may have the effect of degrading combustion stability at idle and light loads because of increased exhaust residual in the engine cylinders. It is known, however, that if the combustion or burn rate is increased, the stability of the combustion at idle will be enhanced, as will the engine's tolerance to exhaust gas recirculation (EGR). Although it is possible to increase burn rate through fixed turbulence devices, such as masked intake valves, this masking or, for that matter, other fixed flow control devices, will decrease the volumetric efficiency of the engine. And, the engine may become excessively noisy or vibration prone at heavy, load, if the burn rate is so great so as to cause an undesirably rapid pressure rise in the combustion chambers. This is sometimes referred to as combustion harshness.
Another problem suffered with some engines is excessive time lag between changes in throttle opening and the engine's torque response. It seems that time response problems arise where a large manifold volume, which may be desirable from the standpoint of allowing tuning of the induction system, must be filled and emptied of air whenever the throttle position is changed.
Problems related to excessive manifold volume and combustion instability at light loads have been solved in prior art engines through the use of individual cylinder port throttles using conventional butterfly valves. Such valves have been employed only for load control; they have not been employed to control charge motion. And, although such valves work well when properly designed and adjusted, such valves have not been used in many high volume production engines because it is difficult to balance airflow between the valves, and such valves are prone to sludging and cause perturbations in airflow.
Port throttles according to the present invention solve the problems associated with prior art throttling devices, while providing the additional benefit of controlling airflow so as to achieve not only load control but also charge motion control, and, as a result, control of the burn rate, which is sometimes termed the combustion rate.